The present invention relates to RF broadcasting and specifically to combining and transmitting adjacent television channels using a common antenna.
In the United States, the Federal Communications Commission (FCC) has established guidelines for broadcasting television signals. At present, the established standard is known as the NTSC signal format which may be broadcast in both the VHF and UHF TV frequency bands. The VHF band includes a low band from 54 MHz to 88 MHz and a high VHF TV band from 174 MHz to 216 MHz. The UHF TV band is from 470 MHz to 806 MHz. The NTSC signal is an analog signal.
The FCC has announced that high definition TV will be forthcoming. It is presently understood that digital television signals (DTV) as well as analog NTSC signals will be simultaneously broadcast for a transitionary period until approximately the year 2006, after which only DTV signals will be broadcast. During the transitionary period the various TV stations that presently broadcast NTSC signals will be allotted a second channel for broadcasting the DTV signals.
Heretofore the FCC has not assigned adjacent NTSC channels to the same location. However, with the need for additional channels for the duration of the transition period, a need arises that adjacent channels may be assigned to the same location wherein at least one channel is a DTV channel.
It will be economical for a station broadcasting both NTSC and DTV signals that the signals be transmitted from a common antenna. This will save the station a significant amount for the cost of erecting a tower (which may be on the order of 1,000 feet tall). A single tower with a common antenna for two or more channels will provide substantial savings.
It is known in the art to employ a common antenna for broadcasting television signals from two non-adjacent NTSC television channels, such as channels 4 and 6 (it is to be noted that channels 4 and 5 are spaced apart by 4 MHz and, hence, are not adjacent channels). For example, the NTSC television signals in channels 4 and 6 have been diplexed and transmitted by a common turnstile antenna in installations in Rochester, N.Y.; Dallas, Tex. and Mexico City as noted on page 122 of an RCA catalog entitled VHF TV Transmitting Equipment, copyright 1968.
It is understood that the FCC has not assigned adjacent NTSC channels to a common area. Generally it is believed that such television signals broadcast from adjacent channels would provide interference with one another. Specifically it is understood that the stronger or higher power channel would dominate the lowerpower channel resulting in artifacts or wavy lines at the receivers of the lower power television signals. In view of these concerns there has been no need thus far to broadcast NTSC signals at adjacent channels. However it is believed that with the advent of digital television there is a need presented to broadcast on adjacent channels, such as adjacent DTV channels or an NTSC channel adjacent to a DTV channel.
It is therefore an object of the present invention to provide for.simultaneous transmission of television signals from adjacent channels with a common antenna.
In accordance with one aspect of the present invention provision is made for transmitting television signals from adjacent channels with a common antenna by providing a source of first television signals from a first channel selected from a first frequency band that includes a plurality of channels. A source of second television signals is provided from a second channel in the first frequency band and wherein the second channel is adjacent to the first channel. The first and second television signals are combined to provide first and second combined signals which are then supplied to a common antenna for transmitting television signals.
In accordance with another aspect of the present invention a radio frequency coupler, such as a combiner, simultaneously couples television signals from a least two television broadcast transmitters for application to a single turnstile type antenna and wherein the television signals are from adjacent frequency channels. The coupler, in accordance with this aspect of the invention, includes a first input circuit for receiving television broadcast signals at a first television frequency from a first broadcast transmitter and a second input circuit for receiving television broadcast signals at a second television frequency channel from a second broadcast transmitter wherein the second channel is located in a television frequency spectrum adjacent to the first channel. A combiner simultaneously receives the broadcast signals from the first and second channels by way of the respective first and second input circuits for purposes of providing combined television broadcast signals including both the first and second adjacent television frequency channels. An output circuit is provided and is adapted to be connected to a turnstile antenna for providing to the antenna the combined television broadcast signals.